assertTrue(result.contains("2021") || result.contains("Jan") || result.contains("1609459200000"));
    }

    // Test appendTimestamp method
    public void test_appendTimestamp() {
        StringBuilder buf = new StringBuilder();

        monitorTarget.appendTimestamp(buf);
        String result = buf.toString();
        assertTrue(result.startsWith("\"timestamp\":\""));
        assertTrue(result.endsWith("\""));

                break;
            case "appendTimestamp":
                appendTimestampMethod = method;
                break;
            case "appendException":
                appendExceptionMethod = method;
                break;
            }
        }

        assertNotNull("Should inherit append method", appendMethod);
        assertNotNull("Should inherit appendTimestamp method", appendTimestampMethod);

            }).collect(Collectors.joining(","));
            buf.append(hotThreads).append(',');
        } catch (final Exception e) {
            appendException(buf, e).append(',');
        }

        appendTimestamp(buf);
        buf.append('}');

        if (logger.isInfoEnabled()) {
            logger.info(buf.toString());
        }
    }

        return buf;
    }

    /**
     * Appends a timestamp to the buffer.
     *
     * @param buf the string buffer to append to
     * @return the updated buffer
     */
    protected StringBuilder appendTimestamp(final StringBuilder buf) {
        final SystemHelper systemHelper = ComponentUtil.getSystemHelper();
        append(buf, "timestamp", () -> FessFunctions.formatDate(systemHelper.getCurrentTime()));
        return buf;
    }

        buf.append("[SYSTEM MONITOR] ");
        buf.append('{');

        appendOsStats(buf);
        appendProcessStats(buf);
        appendJvmStats(buf);
        appendFesenStats(buf);

        appendTimestamp(buf);
        buf.append('}');

        if (logger.isInfoEnabled()) {
            logger.info(buf.toString());
        }
    }

    private void appendJvmStats(final StringBuilder buf) {